The present invention relates to the field of treating ischemic retinopathy, particularly that caused by retinal infarction.
Ischemic retinopathy is a major cause of blindness. Retinal ischemia may result from a number of different causes and may be associated with other diseases and conditions, such diabetes, atherosclerosis, etc. For example, retinal ischemia caused by central retinal vein occlusion (CRVO). CRVO may result from a number of different underlying conditions.
A number of treatments have been suggested for retinal ischemia. For example, to manage outflow obstruction, it has been suggested to administer fibrinolytic agents and anticoagulants, to conduct hemodilution and plasma exchange, to administer steroids, or to conduct photocoagulation. See Kohner et al, "The Management of Central Retinal Vein Occlusion", Ophthalmology, 90(5): 484-487 (1983). Unfortunately, the aforementioned treatments have not been found very effective. See also Hansen et al, "A Randomised Prospective Study on Treatment of Central Retinal Vein Occlusion by Isovolaemic Haemodilution and Photocoagulation", British Journal of Ophthalmology, 69:108-116 (1985).
The prognosis for diabetic retinal angiopathy is not very encouraging. See Buzney et al, "Pathogenesis of Diabetic Retinal Angiopathy: Proposed Mechanisms and Current Research", International Ophthalmology Clinics, 24(4):1-11 (Winter, 1984). Buzney et al recognize that a need exists to develop new methods of treating diabetic retinal angiopathy, suggesting that research efforts will "someday produce chemotherapeutic methods that will exceed the scope of laser or vitreoretinal surgery". Buzney et al hypothesize that the systemic use of such chemotherapeutic agents may be supplemented "by injection into the vitreous chamber or even the use of a vitreous substitute that fully tamponades the retina, inactivating or selecting inhibiting the diffusion of vasoactive substances". See Buzney et al at page 9.
While some of the aetiologies of retinal vein occlusion are well understood, others are only partially so, and in still others the cause remains obscure. Systemic hypertension is recognized as a cause of certain occlusions, as is the inflammation of the vein wall (periphlebitis) and glaucoma. As discussed in Kanski et al, "Disorders of the Vitreous, Retina and Choroid", Ophthalmology I, pp. 115-121, Butterworths International Medical Reviews, London, (1983), the conventional treatments for retinal vein occlusion are systemic drug administration and photocoagulation, neither of which are consistently effective.
Although generally unrelated to the management of central retinal vein occlusion or other retinal ischemias, it is known to introduce a variety of liquids or gases into the ocular globe for a variety of reasons. For example, in Chandler et al, "A Refined Experimental Model for Proliferative Vitreoretinopathy", Graefe's Arch Clin. Exp. Ophthalmol, 224:86-91 (1986), experiments are described wherein the intact vitreous region is injected with large numbers of tissue cultured fibroblasts. However, such injections were not found to induce the disease as it is found in humans. In Lincoff et al, "Use of an Intraocular Gas Tamponade to Find Retinal Breaks", American Journal of Ophthalmology, 96:510-516 (1983), the subretinal fluid was drained and the volume replaced by a perfluorocarbon gas calculated to fill the eye below the probable level of the retinal break. The bubble closed the break and maintained reattachment until the gas was absorbed.
In Kreissig et al, "The Treatment of Difficult Retinal Detachments with an Expanding Gas Bubble Without Vitrectomy", Graefe's Arch. Clin. Exp Ophthalmology 224:51-54 (1986). A prospective study is reported using perfluorocarbon gases (CF.sub.4, C.sub.2 F.sub.6, C.sub.3 F.sub.8) without prior mechanical vitrectomy.
In Haut et al, "Some of the Most Important Properties of Silicone Oil to Explain its Action", Ophthalmologica, Basel 191:150-153 (1985), the action of silicone oil used to close tears and reattach the retina is disclosed. The action of such silicone oil is described as being a result of its density and surface tension causing the bubble to press upon the upper part of the eye, i.e., most of the time at twelve o'clock so there is constant support upwards which closes the tears and reattaches the retina.
Notwithstanding what is known in this area, there is a long felt need for effect methods to treat ischemic retinopathy.